Datasheet > AS1129T3-3.3

AS1129T3-3.3

更新时间： 2024-01-07 11:47:03

品牌	Logo	应用领域
西伯斯 - SIPEX		输出元件调节器
页数	文件大小	规格书
4页	120K
描述
Fixed Positive LDO Regulator, PSSO5, TO-263, 5 PIN

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AS1129T3-3.3 技术参数

是否Rohs认证：	不符合	生命周期：	Obsolete
包装说明：	TO-263, 5 PIN	Reach Compliance Code：	unknown
风险等级：	5.76	JESD-30 代码：	R-PSSO-G5
湿度敏感等级：	1	端子数量：	5
封装主体材料：	PLASTIC/EPOXY	封装形状：	RECTANGULAR
封装形式：	SMALL OUTLINE	峰值回流温度（摄氏度）：	225
认证状态：	Not Qualified	调节器类型：	FIXED POSITIVE SINGLE OUTPUT LDO REGULATOR
表面贴装：	YES	端子形式：	GULL WING
端子位置：	SINGLE	处于峰值回流温度下的最长时间：	NOT SPECIFIED
Base Number Matches：	1

AS1129T3-3.3 数据手册

AS1129

Also, it may be programmed for any output voltage between its

1.235V reference and its 30V maximum rating. As seen in

Figure 2, an external pair of resistors is required.

Refer to the below equation for the programming of the output

voltage:

REDUCING OUTPUT NOISE

It may be an advantage to reduce the AC noise present at the output.

One way is to reduce the regulator bandwidth by increasing the size of

the output capacitor. This is the only way that noise can be reduced

on the 3 lead AS1129 but is relatively inefficient, as increasing the

capacitor from 1µF to 220µF only decreases the noise from 430µV to

160µV Vrms for a 100kHz bandwidth at 5V output.

_OUT= V_REF× (1 + R₁/ R₂)+ I_FBR₁

Noise could also be reduced fourfold by a bypass capacitor across R₁,

since it reduces the high frequency gain from 4 to unity. Pick

The V_REFis 1.235 and I_FBis the feedback bias current, nominally

-20nA. The minimum recommended load current of 1 µA forces

an upper limit of 1.2 MΩ on value of R₂. If no load is presented

the I_FBproduces an error of typically 2% in V_OUT, which may be

eliminated at room temperature by trimming R₁. To improve the

accuracy choose the value of R2 = 100k this reduces the error by

0.17% and increases the resistor program current by 12µA. Since

the AS1129 typically draws 60 µA at no load with Pin 2 open-

circuited this is a small price to pay

_BYPASS≅ 1 / 2πR₁× 200 Hz

or choose 0.01µF. When doing this, the output capacitor must be

increased to 3.3µF to maintain stability. These changes reduce the

output noise from 430µV to 100µV Vrms for a 100kHz bandwidth at

5V output. With the bypass capacitor added, noise no longer scales

with output voltage so that improvements are more dramatic at higher

output voltages.

HEAT SINK REQUIREMENTS

Depending on the maximum ambient temperature and maximum

power dissipation a heat sink may be required with the AS1129.

The junction temperature range has to be within the range

specified under Absolute Maximum Ratings under all possible

operating conditions. To find out if a heat sink is required, the

maximum power dissipation of the device needs to be calculated.

This is the maximum specific AC voltage that must be taken into

consideration at input. Figure 3 shows the condition and power

dissipation which should be calculated with the following

formula:

I_IN

V_OUT

OUT

I_L

_TOTAL= (V_IN- 5) * I_L+ (V_IN) I_G

AS1521

Next step is to calculate the temperature rise T_R(max). T_J(max)

maximum allowable junction temperature, T_A(max) maximum

ambient temperature :

LOAD

2.2uF

GND

I_G

T_R(max) = T_J(max) - T_A(max)

I_IN= I_L+ I_G

Junction to ambient thermal resistance θ_(J-A)can be calculated

after determining of P_{TOTAL &}T_R(max):

Figure 3. Fixed +5V Regulator Circuit

θ_(J-A)= T_R(max)/P_(max)

If the θ_(J-A)is 60°C/W or higher, the device could be operated

without a heat sink. If the value is below 60°C/W then the heat

sink is required and the thermal resistance of the heat sink can be

calculated by the following formula, θ_(J-C)junction to case, θ_(C-H)

case to heat sink, θ_(H-A)heat sink to ambient:

θ_(J-A)= θ_(J-C)+ θ_(C-H)+ θ_(H-A)

Rev. 10/11/00

1 2 34

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